In commercial, industrial and domestic applications it is often useful to determine quickly the position, speed or direction of rotation of a movable body such as a meter hand, a robot arm, or perhaps an abnormality in a plate of dielectric material. For an example of the former, various means have been developed for determining the position of the dial hands of utility meters so as to permit them to be read rapidly and automatically from a remote location. In contrast with conventional practice in which a utility company employee periodically visits each meter to obtain a visual reading, remote meter reading offers very significant economic benefits. By suitable means, for example, all the meters in a large apartment complex can be read in a few seconds from a single location outside the building or in the basement; or meters can be read several times daily to allow the utility to obtain energy flow data, study consumption patterns, or (by the use of time-of-day rates) discourage consumption during periods of high demand.
Clearly, in such a reading means a highly desirable feature is the ability to read ordinary utility meters which are already in service. Nonetheless, with the exception of previous work by and on behalf of the assignee of this application, remote meter dial reading has been generally possible only through the use of expensive specially-equipped meters which replaced the ordinary meter already in use. The above-mentioned previous efforts by and on the part of the assignee have resulted in meter-reading systems disclosed in U.S. Pat. Nos. 3,500,365, 4,433,332 and 4,007,454; and in U.S. patent application Ser. No. 375,919, filed May 7, 1982, and now abandoned. In each of these patents and applications, in general, a sensing transducer scans the dials of the meter by inducing an electric or magnetic field which includes the hands. The theory of the aforementioned patents and applications is that the transducer's field can be coupled to the meter hand through the intervening space, and variations in the phase of the resultant signal detected give an indication of the meter hand's position. Because no mechanical parts that move relative to one another are used, potential problems of maintenance and reliability are eliminated.
Improvements to the devices disclosed in the above-mentioned patents and applications are also disclosed in U.S. Pat. No. 4,429,308 assigned to the assignee of this application. This application is directed to a peculiar shape of the field-producing electrode which provides improved uniformity of angular sensitivity. Also, a further improvement is disclosed in U.S. Pat. No 4,214,152, issued July 22, 1980, which involves a technique for compensation for the mechanical misalignment of one of a plurality of meter hands by adjusting the reading of a more significant hand responsive to the hand position of the adjacent lesser significant integer.